Elevated Oxide Ratio in ICP-MS

Answer

This Information Applies To: Agilent ICP-MS systems (7700/7800/7850/7900/8800/8900)

Issue

Elevated oxide ratio values are defined as greater than 1.5% for x-lens configuration or greater than 3% for s-lens configuration. Possible causes are contamination, or a fault with the sample introduction system.

Background

The Oxide Ratio (%) is defined as: mass 156 (CeO) / 140 (Ce) x 100

Gd, Dy, CdAr, SnAr, and SeSe are some examples of contaminants/interferences that contribute to elevated counts on mass 156.

Items Required

• Tuning Solution for ICP-MS 1 ppb (p/n 5185-5959), or 
• Tuning Solution for ICP-MS 10 ppb (p/n 5184-3566)
• Type I de-ionized water
• Trace metal grade Nitric Acid
• Spare Sample Introduction Components

Steps to Follow

Check for Contamination

1. Prepare or pour fresh tuning solution in 1% HNO₃ (1 ppb tuning solution for standard configuration, 10 ppb tuning solution for ISIS 3 configuration)

2. Place the internal standard line into a fresh 1% HNO₃ rinse solution (for standard configuration) or place the carrier line into a fresh 1% HNO₃ rinse solution (for ISIS 3 configuration).

3. Light plasma and perform startup tasks: Torch Axis, EM, Plasma Correction, Standard Lenses Tue, Resolution/Axis, and Performance Report.

4. Check the oxide ratio from the startup performance report. If the oxide ratio has decreased, either the tuning solution or rinse solution was contaminated.

5. If the oxide ratio has not decreased, it is possible that the de-ionized water source, or HNO₃ source is contaminated. Prepare again the tuning solution and 1% HNO₃ rinse solution with a second source of de-ionized water and HNO₃, then retest.

6. If the high oxide ratio occurred after replacing the argon, the contamination could be in the argon gas. Contact your gas supply company and test a different source of argon.

7. It is also possible that the sample introduction system is contaminated. Clean the nebulizer, spray chamber, torch, cones, and lens stack as per the Agilent ICP-MS Hardware Maintenance Manual. See the ICP-MS MassHunter Help and Learning Center. See the article Access Agilent ICP-MS User Manuals with MassHunter 5.x for accessing the Help and Learning Center.

Check for Sample Introduction Fault

1. If the high oxide ratio occurred after sample introduction maintenance, please confirm that the torch, spray chamber, nebulizer, cones, and lenses have been reinstalled properly.

2. The oxide ratio should increase when you increase the nebulizer (carrier) gas flow. Check the nebulizer gas connection and replace the nebulizer if needed.

3. Verify that the cones are in good condition. Poor orifice shape or size, or excessively dirty cones can cause elevated oxide ratio. Replace the skimmer and sampler cone if needed.

Learn how to effectively troubleshoot your Agilent ICP-MS System: Agilent 7800/7850/7900 ICP-MS with MassHunter e-learning course available from Agilent education